It is common practice in the electronics industry to subject integrated circuit chips to testing prior to their being placed in service and prior to their being encapsulated, or otherwise mounted, in an integrated circuit package having leads extending therefrom which connect the terminal areas of the chip to circuitry on a circuit board or the like. Such preliminary testing or "burning-in" is quite often used when the IC chip is to be employed in a critical circuit and under circumstances where its replacement, should it prove to be defective, would involve expensive reworking of the equipment in which it is installed. The IC packages used for these testing procedures can have conventional lead frames therein which require that the connections between the conductors of the package, the leads, and the terminal areas of the chip be made by wire bonding methods. This procedure is not desirable for the reason that the wires, which must be bonded to the chip for the testing operation, must later be removed from the chip and damage to the chip can result. It has been suggested that the IC package used for the testing process be provided with bumps or promontories on its leads so that the chip can be simply positioned against the bumps thereby to establish contact with the terminal areas. At the conclusion of the testing process, the chip can be easily removed from the IC test package and placed in service with full confidence in its future performance.
Attempts thus far to produce a package having such contact bumps thereon have not been highly successful for the reason that it is extremely difficult to produce the bumps or promontories on the ends of the conductors of the IC package. These bumps must be quite small, must be precisely located so that they will contact the terminal areas of the chip, and they must be of uniform height so that the chip will lie flat on a cluster of bumps with one bump in electrical contact with each terminal area of the chip. The present invention is directed to an improved integrated circuit package having contact promontories or bumps which satisfy all of these requirements.
An integrated circuit package in accordance with the invention comprises an insulating substrate of molded plastic material having a flat surface and having a plurality of electrodeposited conductors embedded therein with the surfaces of these conductors being coplanar with the flat surfaces. The inner ends of the conductors extend from a centrally located chip-receiving zone and generally spherical contact promontories or bumps are provided on these inner ends. The bumps or promonotories are of uniform height above the flat surface and they are precisely located so that a chip can be placed on the bumps and the bumps will be in contact with the terminal areas of the chip. The chip can be temporarily held on the package by means of a suitable clip and upon connecting the outer ends of the conductors to suitable test circuitry, the chip can be tested and then removed from the package and placed in service.
Integrated circuit packages in accordance with the invention are produced by etching hemispherical depressions in unmasked portions of one surface of an etchable metal, such as copper, having masking or resist material extending over the remainder of its surface. After etching of the depressions, the resist material is removed along paths which correspond to the paths of the conductors in the finished IC package. Thereafter, conductive metal is deposited against the copper in the unmasked portions of the etchable metal including the depressions. The masking material is then totally removed. Molding material is then molded against the etchable metal surface so that the conductors are embedded in the molding material which forms the substrate. Finally, the etchable metal is etched away leaving a flat surface on the substrate in which the conductors are embedded with the bumps projecting above this flat surface as hemispherical projections.